Don't override start_output() function in GUI logger to correctly reset statistics.

doc/changelog.txt

@@ -1,5 +1,8 @@
 6.9 "" (released xx.xx.2011)
 
+Fixes:
+- gui: Correctly reset logger statistics.
+
 Changes:
 - checking: Automatically allow redirections from URLs given by the
   user.

linkcheck/gui/logger.py

@@ -56,7 +56,3 @@ class GuiLogger (Logger):
     def end_output (self):
         """Emit statistic data which gets logged in the main window."""
         self.log_stats_signal.emit(self.stats)
-
-    def start_output (self):
-        """Override output handling of base class."""
-        pass